The present invention relates to an amplifier circuit and a mixer circuit. More specifically, the present invention relates to the improvement of linearity of active devices, which can be degraded by the trans-conductance thereof.
As RF amplifier is integrated into a transceiver chip, the linearity requirement per unit DC power consumption is getting more stringent.
Generally, in the CDMA (Code Division Multiple Access) communications, a transmitter and a receiver are isolated by means of a duplexer. Because the maximum output power reaches up to 28 dBm while a duplexer can attenuates only around 40 dB, the spurious signals of transmitter act as main interference source. Occasionally, these signals appear in receive band by means of either inter-modulation or cross-modulation. This is the most outstanding reason which caused the recent stringent linearity requirement for LNA (Low Noise Amplifiers).
Various solutions for improving the linearity of amplifiers have been developed especially in system level. Among the solutions, there are pre-distortion, feed-forward, Cartesian feedback, and so on. However, those solutions require complex hardware. Therefore, while those solutions may be employed in a large system such as a base station, they are not suitable to be employed in a small system such as a handset.
Until now, linearization techniques have been mostly applied to power amplification field. However, because of the above reasons, linearization of other RF circuit blocks are required. As LNAs, mixers and driver amplifiers are being integrated in one-chip, the linearity itself and linearity per unit DC power consumption becomes important figure of merit for a circuit block.
An object of the invention is to provide an amplifier circuit having a active device, whose linearity is improved.
Another object of the invention is to provide an amplifier circuit whose non-linearity due to trans-conductance of active devices is suppressed.
Further object of the invention is to provide a Cascode type amplifier circuit whose non-linearity due to trans-conductance of active devices is suppressed.
Still further object of the invention is to provide a mixer circuit whose non-linearity due to trans-conductance of active devices is suppressed.
In order to accomplish the objects, the present invention provides an amplifier circuit comprising: a main active device having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal varies depending on voltage driven to the first terminal; an auxiliary active device having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal is varies depending on voltage driven to the first terminal; a main biasing unit connected to the first terminal of said main active device, the third terminal; of said main active device, voltage source, an input terminal, and an output terminal, by which said main active device operates primarily in a saturation region; and an auxiliary biasing unit connected to the first terminal of said auxiliary active device, the third terminal of said auxiliary active device, voltage source, an input terminal, and an output terminal, by which said auxiliary active device operated primarily in a sub-threshold region.
According to another aspect of the present invention, a compensation circuit for compensating non-linearity of a main active device having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal is varying in dependant on voltage driven to the first terminal, is provided. The compensation circuit comprises: an auxiliary active device having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal is varying in dependant on voltage driven to the first terminal; and a biasing unit connected to the first terminal of the auxiliary active device, the third terminal of the auxiliary active device, voltage source, an input terminal, and an output terminal, by which the auxiliary active device operates primarily in sub-threshold region under condition that the main active device operates primarily in saturation region.
According to further aspect of the present invention, an amplifier circuit is provided, which comprises: first and second main active devices having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal is varying in dependant on voltage driven to the first terminal, and the first and second active devices are serially coupled such that the third terminal of the first active device is coupled to the second terminal of the second active device; an auxiliary active device having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal is varying in dependant on voltage driven to the first terminal, and the third terminals of the first main active device and the auxiliary active device are connected; and a biasing unit connected to the first terminals of the first and second main active devices, the first terminal of the auxiliary active devices, the third terminal of the second main active device, voltage source, an input terminal, and an output terminal, by which the first and second main active devices operate primarily in saturation region and the auxiliary active device operates primarily in sub-threshold region.
According to still further aspect of the present invention, a mixer circuit is provided, which comprises: a main active device having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal is varying in dependant on voltage driven to the first terminal, an active device pair comprising two active devices having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal is varying in dependant on voltage driven to the first terminal, and wherein the first active device and the active device pair is serially coupled such that the third terminal of the first active device is coupled to the second terminals of the active devices in the active device pair; an auxiliary active device having first, second, and third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal is varying in dependant on voltage driven to the first terminal, and the third terminals of the first main active device and the auxiliary active device are connected; and a biasing unit connected to the first terminals of the main active device and the active devices in the active device pair, the first terminal of the auxiliary active device, voltage source, an input terminal, and an output terminal, by which the main active device operates primarily in saturation region and the auxiliary active device operates primarily in sub-threshold region.